1. Field of the Invention
The present invention relates to an anti-reflective polymer that is useful in a submicrolithographic process, a composition comprising the polymer, and a method for preparing the same. In particular, the present invention relates to a polymer that can be used in an anti-reflective coating layer to reduce or prevent back reflection of light and/or to eliminate the standing waves in the photoresist layer during a submicrolithographic process. The present invention also relates to a composition comprising the polymer, and a method for using the same.
2. Description of the Prior Art
In most submicrolithographic processes standing waves and/or reflective notching of the waves typically occur due to the optical properties of the lower layer coated on a substrate and/or due to changes in the thickness of a photosensitive (i.e., photoresist) film applied thereon. In addition, typical submicrolithographic processes suffer from a problem of CD (critical dimentional) alteration caused by diffracted and/or reflected light from the lower layer.
One possible solution is to apply an anti-reflective coating (i.e., ARC) between the substrate and the photosensitive film. Useful ARCs have a high absorbance of the light wavelengths that are used in submicrolithographic processes. ARCs can be an inorganic an organic material, and they are generally classified as xe2x80x9cabsorptivexe2x80x9d or xe2x80x9cinterferingxe2x80x9d depending on the mechanism. For a microlithographic process using I-line (365 nm wavelength) radiation, inorganic anti-reflective films are generally used. Typically, TiN or amorphous carbon (amorphous-C) materials are used for an absorptive ARC and SiON materials are typically used for an interfering ARC.
SiON-based anti-reflective films have also been adapted for submicrolithographic processes that use a KrF light source. Recently, use of an organic compound as ARC has been investigated. It is generally believed that an organic compound based ARCs are particularly useful in submicrolithographic processes, in particular those using an ArF light source.
In order to be useful as an ARC, an organic compound needs to have many diverse and desirable physical properties. For example, a cured ARC should not be soluble in solvents because dissolution of the organic ARC can cause the photoresist composition layer to peel-off in a lithographic process. One method for reducing the solubility of cured ARC is to include cross-linking moieties such that when cured the ARC becomes cross-linked and becomes insoluble in most solvents used in lithographic processes. In addition, there should be minimum amount of migration (i.e., diffusion), if at all, of materials, such as acids and/or amines, to and from the ARC. If acids migrate from the ARC to an unexposed area of the positive photoresist film, the photosensitive pattern is undercut. If bases, such as amines, diffuse from the ARC to an unexposed area of the positive photoresist film a footing phenomenon occurs. Moreover, ARC should have a faster etching rate than the upper photosensitive (i.e., photoresist) film to allow the etching process to be conducted smoothly with the photosensitive film serving as a mask. Preferably, an organic ARC should be as thin as possible and have an excellent light reflection prevention property.
While a variety of ARC materials are currently available, none of these materials is useful in ArF laser submicrolithographic processes. In the absence of an ARC, the irradiated light penetrates into the photoresist film and is back reflected or scattered from its lower layers or the surface of the substrate (e.g., semiconductor chip), which affects the resolution and/or the formation of a photoresist pattern.
Therefore, there is a need for an ARC material which have a high absorbance of the wavelengths used in submicrolithographic processes.
It is an object of the present invention to provide an organic polymer that can be used as an ARC material in ArF laser (193 nm) or KrF laser (248 nm) submicrolithographic processes.
It is another object of the present invention to provide a method for preparing an organic polymer that reduces or prevents diffusion and/or light reflection in submicrolithography processes.
It is a further object of the present invention to provide an ARC composition comprising such an organic diffusion/reflection preventing or reducing polymer and a method for producing the same.
It is a still further object of the present invention to provide a method for producing a photoresist pattern using ArF laser submicrolithographic processes with reduced standing wave effect.
It is yet another object of the present invention to provide a semiconductor device which is produced using the ARC composition in a submicrolithographic process.
Alkyl groups according to the present invention are aliphatic hydrocarbons which can be straight or branched chain groups. Alkyl groups optionally can be substituted with one or more substituents, such as a halogen, alkenyl, alkynyl, aryl, hydroxy, amino, thio, alkoxy, carboxy, oxo or cycloalkyl. There may be optionally inserted along the alkyl group one or more oxygen, sulfur or substituted or unsubstituted nitrogen atoms. Exemplary alkyl groups include methyl, ethyl, i-propyl, n-butyl, t-butyl, fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, trichloromethyl, and pentafluoroethyl.
In a submicrolithography process, an anti-reflective coating (i.e., ARC) is used to reduce or prevent the standing wave effect and/or reflective notching which can occur upon exposure of a photosensitive layer to light. In addition, the ARC reduces or eliminates the influence of a back diffraction and reflection of light from the lower layer. The ARC can also prevent undercutting and footing problems which can occur upon forming images on photosensitiveimaterials. To be useful, the ARC must have a high absorbance at specific wavelengths.
The present invention provides polymers that comprise a chromophore substituent which is highly absorptive of light, in particular at wavelengths of 193 nm and 248 nm. Polymers of the present invention can further comprise a crosslinking moiety. It has been found by the present inventors that the presence of such cross-linking moiety significantly improves the adhesiveness and dissolution of the ARC. Useful cross-linking moieties include an epoxide moiety. Without being bound by any theory, it is believed that heating (i.e., baking) ARC causes opening of the epoxide ring and creates crosslinking within the ARC polymer, thereby improving the physical properties of the ARC. In particular, uncured ARC resins (i.e., polymers) of the present invention are soluble in most hydrocarbon solvents, thus allowing ARC resins to be easily coated onto a substrate. However, a cured (i.e., baked) ARC of the present invention are relatively insoluble in most solvents, thus preventing dissolution of the ARC in a developing solution. It is believed that ARCs of the present invention have higher etching rate than ArF photosensitive films because the crosslinking moieties are bonded to each other via Cxe2x80x94O linkages. This higher etching rate significantly improve is in the etch selection ratio between the ARC and the photosensitive film.
In one aspect of the present invention, an anti-reflective coating polymer is selected from the group consisting of a polymer of the formula: 
and mixtures thereof,
wherein
Ra, Rb, Rc, Rd, and Re are independently hydrogen or C1-C6 alkyl (preferably methyl);
R1 to R4 are independently hydrogen, optionally substituted C1-C5 alkyl, or optionally substituted alkoxyalkyl;
R5 is hydrogen, hydroxide, a moiety of the formula xe2x80x94COCH3, optionally substituted C1-C4 alkyl, optionally substituted cycloalky, optionally substituted alkoxyalky, or optionally substituted cycloalkoxyalkyl;
w, x, y and z are mole fractions each of which is independently in the range of from 0.1 to 0.9; and
each of l, m, n, and p is independently an integer of 1 to 3.
The terminal groups of a polymer depicted in the present disclosure depend on the particular polymerization initiator used. In addition, as used throughout this disclosure, it should be appreciated that the order of monomeric units represented in a polymer formula does not necessarily indicate the actual order of such monomeric units in the polymer. Monomeric units represented in a polymer formula are intended to simply indicate the presence of such monomeric units in the polymer. Moreover, the variables represent the total relative ratio of each unit. For example, the total amount xe2x80x9cwxe2x80x9d in Formula 1 above can be inter dispersed throughout the polymer (not necessarily in same concentrations) or all or majority of such polymeric unit can be concentrated in one particular location of the polymer.
Another aspect of the present invention provides a method for producing an anti-reflective coating polymer, such as those described above.
In one particular embodiment of the present invention, the polymer of Formula 1 is produced by polymerizing a mixture of monomers comprising:
a 4-(4-hydroxyphenoxy)acetoxyalcoholacrylate monomer of the formula: 
a hydroxyalkylacrylate monomer of the formula: 
an alkylacrylate monomer of the formula: 
and a glycidylacrylate monomer of the formula: 
in the presence of a polymerization initiator, where Ra, Rb, Rc, Rd, Re, R1 to R4, l, m, n and p are those defined above. Each of the monomers is present in a mole fraction ranging from about 0.1 to about 0.9.
Another embodiment of the present invention provides a method for producing the polymer of Formula 2 from a mixture of monomers comprising:
4-(4-hydroxyphenyl)pyruvicalcoholacrylate monomer of the formula: 
the hydroxy alkylacrylate monomer of Formula 15, the alkylacrylate monomer of Formula 16, and the glycidyl acrylate monomer of Formula 17 described above in the presence of a polymerization initiator, where Ra, R1 to R4, l, and p are those defined above. Each of the monomers is present in a mole fraction ranging from about 0.1 to about 0.9.
Yet another embodiment of the present invention provides a method for producing the polymer of Formula 3 from a mixture of monomers comprising:
a vinyl 4-benzoateketone monomer of the formula: 
the hydroxy alkylacrylate monomer of Formula 15, the alkylacrylate monomer of Formula 16, and the glycidyl acrylate monomer of Formula 17 described above in the presence of a polymerization initiator, where Ra, R1 to R5, and l are those defined above. Each of the monomers is present in a mole fraction ranging from about 0.1 to about 0.9.
Preferably, mixtures of monomers described above further comprise an organic solvent. Useful organic solvents in polymerization are well known to one of ordinary skill in the art. In particular, a polymerization solvent is selected from the group consisting of tetrahydrofuran, toluene, benzene, methylethyl ketone, dioxane, and mixtures thereof.
Useful polymerization initiators include those well known to one of ordinary skill in the art, such as 2,2-azobisisobutyronitrile (AIBN), acetylperoxide, laurylperoxide and t-butylperoxide.
Preferably, the polymerization reaction is conducted at temperature in the range of from about 50xc2x0 C. to about 80xc2x0 C.
Another aspect of the present invention provides an ARC composition comprising a polymer the Formula 1, 2, 3, or mixtures thereof. It has been found by the present inventors that such an ARC composition is particularly useful in a submicrolithography process. The ARC composition can further include an organic solvent.
Still another aspect of the present invention provides a method for producing the ARC composition described above comprising the steps of admixing the ARC polymer described above with an organic solvent. Useful organic solvents for ARC composition include conventional organic solvent. Preferred organic solvents for ARC composition include ethyl 3-ethoxypropionate, methyl 3-methoxypropionate, cyclohexanone, propylene glycol methyletheracetate, and mixtures thereof. The amount of organic solvents for ARC composition is preferably in the amount of from about 200 to about 5,000% by weight relative to the total weight of the ARC polymers used.
Further aspect of the present invention provides a method for forming an ARC on a substrate. In one embodiment, the ARC compositing described above is coated on a substrate, such as a wafer, and the coated substrate is heated (e.g., baked). The ARC composition can be filtered prior to being coated onto the substrate. Heating of the coated substrate is preferably conducted at temperature in the range of from about 100xc2x0 C. to about 300xc2x0 C. for a period of from about 10 sec. to about 1,000 sec. Heating the coated substrate produces a film of crosslinked ARC polymer.
It has been found by the present inventors that the ARCs of the present invention exhibit high performance in submicrolithographic processes, in particular using KrF (248 nm), ArF (193 nm) and F2 (157 nm) lasers as a light source.
In accordance with yet another aspect, the present invention provides a semiconductor device produced using the ARC composition described above.